Implantable electrical stimulation systems have proven therapeutic in a variety of diseases and disorders. For example, spinal cord stimulation systems have been used as a therapeutic modality for the treatment of chronic pain syndromes. Peripheral nerve stimulation has been used to treat chronic pain syndrome and incontinence, with a number of other applications under investigation. Functional electrical stimulation systems have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Stimulators have been developed to provide therapy for a variety of treatments. A stimulator can include a control module (with a pulse generator), one or more leads, and an array of stimulator electrodes on each lead. The stimulator electrodes are in operational contact with or near the nerves, muscles, or other tissue to be stimulated. The pulse generator in the control module generates electrical pulses that are delivered by the electrodes to body tissue.
Conventional implanted electrical stimulation systems are not safe in magnetic resonance imaging (MRI) environment due to the high strength magnetic field and the fluctuations in the magnetic fields caused by radio frequency (RF) pulses used during the MRI procedure. The leads have the permittivity and the conductivity different from that of the interstitial fluid. During the MRI scan, the magnetic fields generated by the RF pulses interact with the lead and induce eddy currents thereby creating unwanted heating of the lead and hence damaging the surrounding tissue. The interaction may also lead to undesired functioning of the electronic components, thereby delivering deleterious stimulations, or premature failure of electronic components.